A continuously variable transmission including a continuously variable speed change mechanism and a subtransmission mechanism is known. The subtransmission mechanism capable of shifting between two forward gear positions is connected in series to an output shaft of the continuously variable speed change mechanism, and by shifting the subtransmission mechanism in accordance with operating conditions, a speed ratio range that can be realized by the continuously variable transmission is enlarged.
In this kind of continuously variable transmission, when the subtransmission mechanism is shifted from a low speed gear to a high speed gear while a vehicle is traveling, shift shock is caused by variation in a through speed ratio, which is the overall speed ratio of the continuously variable transmission. In JP05-79554A, control is performed to keep the through speed ratio constant by increasing the speed ratio of the continuously variable speed change mechanism rapidly in alignment with a shift in the subtransmission mechanism.